Stabilization of polyvinyl acetal resins



Patented May 23, 1939 STABILIZATION F POLYVINYL ACETAL RESINS Charles R. Fordyce and Martti Salo; Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey No Drawing. Application August 1 4, 1937,

Serial N0. 159,193

8 Claims. (01. 26l'l---'I3) This invention relates to the stabilization of in viscosity upon heating of an unstabilized polya polyvinyl acetal resin by subjecting either its vinyl acetal resin: polyvinyl intermediate or the resin itself to the action of nitrous acid which is usually applied in Original "Viscosity alter the form of its salt under acid conditions. The viscosit heating for 24 5 y hours at 110 0. treatment of the resin may take place either in (fientlpo sesi (campuses) the reaction mixture, during its preparation, just prior to its precipitation from the reaction mix- 209 ture, or on the resin itself after separating it from flm m fl whim 199 10 its reaction constituents. 102

The instability of -polyvinyl acetal resins has. been a Problem in the art of m in 5 8 We have found that by subjecting either the t yp of r s For instance. a productcan polyvinyl intermediate, such as polyvinyl alcohol be made therefrom and s e late! the D or polyvinyl acetate, to the action of nitrous acid 15 Ilet y o e k and de d. t in the reaction mixture employed to prepare the 15 milleting its commercial e esspoiyvinyl acetal resin or by the treatment of the One Object f o r in enti n is o prep p iypolyvinyl acetal resin after its formation, a resin v y a etal r s ns wh h d n t exhi t a t ndis formed "which exhibits good stability as eviy to degrade p aging or darken when heatdenced by testing it by the methods outlined ed. Another object of our invention is to render; above. Thus, polyvinyl acetal resins, which have 20, po y y eeetel s s le 5 t t y y he been stabilized by our invention, can be employed employed for use in making commercial products t prepare commercial products without any Whose life is not shortened by the breakdown of darkening or degradation occurring in use. These e resin Which might Otherwise 1 W hout stabilized acetal resins are particularly adapted a stabilization treatment such as in accordance to use in the commercial arts, such as in the 25 with our invention. making of photographic film.

The st y f p y y aeetal s s may Owing to the comparative instability of polybe manifested in Various ys, Such as by the vinyl acetal'resins, it is preferred that the treatbrittleness and increased color of an aged film of me t with the stabilizing agent'occur prior to the resin- This characteristic Course. Ve y the heat-drying of the resin which occurs after. 30 detrimental in most cases where a resin film may e rati it from it reaction 1 t If 1 be p y sired, the treatment may be applied before the In the laboratory the emelmt of St bi ty is washing of the resin so that the" stabilizing comdetermined by subjecting the product to an elepound will thereby be removed along with the 5 vated temperature for a prescribed period of time. other materials with which it is in contact. Nev- One method of determining the stability is by ertheless,acompound as described will, also, have heating a sample of the resinto a temperature a, stabilizing effect if used as a stabilization treatof about 180 C. in a stream of nitrogen and ment to the resin after it has been heat-dried, measuring the decomposition products formed. but preferably beforethe resin has been stored These products are formed by passing the gases for a length of time sufiicient to result in de- 40 given off over heated copper oxide which oxidizes gradation.

these gases carbon dioxide and e W e- We have found that it is unnecessary, however, upon' the carbon dioxide gas is collected and that the stabilizing compound remain incorpo- W drated in the resin, the only requirement being Our preferred method of ascertaining stability that the resin or its polyvinyl intermediate be 45 is to heat a sample of the resin at about 110 C. treated therewith either after its formation or for 24-. hours and then measure the'loss of visduring its preparation. 0 cosity of a 5% solution of the resin inacetic acid. We have found that the most suitable quan- The viscosity may be determined in any custity of nitrous acid to employ is approximately tomary manner, such as by the use of a viscosi- 1%, based on the weight of the polyvinyl inter- 50 meter. In this test a polyvinyl acetal resin, which mediate employed in the reaction mixture. has not been stabilized, shows a decided drop in Quantities which are distinctly below 1% do not viscosity. The following data illustrates the drop give satisfactory stabilization. It is preferred that a quantity of nitrite not above 5%, based on the weight of the polyvinyl intermediate, be employed, as above that amount the nitrite is not soluble in many of the useful reaction solvents and, therefore, would tend to separate from the solution. Where no question of solvents is involved, such as where the resin itself after separation from the reaction mixture is being treat ed, larger amounts of the nitrite may be employed as well as those proportions given.

The following examples illustrate the preparation of stable polyvinyl acetal resins in accordance with our invention:

Example I 150 parts of polyvinyl acetate was dissolved in 450 parts of ethyl alcohol. There was then added to this solution 75 parts of paraldehyde, 37 parts of concentrated hydrochloric acid and 1% parts of sodium nitrite. The solution was maintained at 40 C. for 4 days. It was then precipitated into water and the precipitated product was washed and dried. The viscosity of the dried polyvinyl acetal resin was not changed by heating 24hours at C. A similar resin prepared in the same' way, excepting that no sodium nitrite was added, showed a drop in viscosity upon heating 24 hours at 110 C. to about A that of the original sample.

Example II formed had a viscosity of 687 cps. as compared with a viscosity of 760 cps. before it was heated.

Example III parts of polyvinyl acetate was dissolved in 450 parts of 70% acetic acid. A mixture of 37.5 parts of 35% hydrochloric acid, 31.5 parts of paraformaldehyde and 1.5. parts of sodium nitrite, dissolved in 20 parts of 50% alcohol, was added thereto. The reaction mixture was allowed to stand at 40 C. for 4. days. The resulting polyvinyl formal was separated therefrom by precipitating into water, washing and drying. The resin had a viscosity of 167 cps. when dissolved in acetic acid. A sample of the resin was heated for 24 hours at 110 C. and the viscosity of the treated resin was found to be. 183 cps.

Example IV The procedure outlined in Example III was followed except that the sodium nitritewas added just prior to the precipitation of the reaction mixture with water instead of at the beginning of the reaction. .The product gave a viscosity before heating of 172 cps. and after heating of cps.

Example V the precipitation of the resin.

Example VI 150 parts of polyvinyl acetate was dissolved in 450 parts of isopropyl alcohol. There was then added thereto 25 parts of sulfoacetic acid dissolved in an equal quantity of water and 75 parts of paraldehyde, and 1 parts of sodium nitrite, dissolved in 20 parts of 50% alcohol. The whole was allowed to stand at 40 C. for 7 days. The resulting polyvinyl acetal resin was found to have a viscosity of 58 cps. before heating and 55 cps. after heating for 24 hours at 110 C.

Example VII Example VI was duplicated except that 20 parts of concentrated sulfuric acid, dissolved in an equal quantity of water, was employed as the catalyst instead of the sulfoacetic acid. The resulting polyvinyl acetal resin had a viscosity of 68 cps. before heating and 59 cps. after heating for 24 hours at 110 C.

Example VIII Example VI was duplicated except that 25 parts of 35% hydrochloric acid was employed as the catalyst instead of the mixture of sulfoacetic acid and water. The resulting resin had the same viscosity after heating for 24 hours at 110 C. as it did before heating.

Example IX 150 parts of polyvinyl acetate was dissolved in 375'parts of ethyl alcohol. The following was then added: 37.5 parts of 35% hydrochloric acid, 37.7 parts of butyraldehyde, 53.8 parts of paraldehyde and a solution of 1.5 parts of sodium nitrite in 20 parts of 50% alcohol. The resulting mixture was held at 40 C. for 4 days. The resulting polyvinyl butyracetal resin was separated therefrom by precipitating into water, washing and drying. The viscosity before heating was 110 cps. and after heating for 24 hours at 110 C. was 103 cps. I

Example X Example IX was duplicated except that the sodium nitrite solution was added to the reaction mixture just before the precipitation of the reaction product into water. The viscosity of the resin was 98 cps. before heating and 64 cps. after heating for 24 hours at 110 C.

Example XI Example IX was duplicated except that 35.2 parts of benzaldehyde was employed instead of the butyraldehyde. The viscosity of the resulting resin was found to be substantially the same after heating for 24 hours at 110 C. as before.

Example XII Example X! was duplicated except that the sodium nitrite solution was added just prior to The viscosity of the resin after heating for 24 hours at 110 C. was found to be substantially the same as before heating.

Other salts of nitrous acid, particularly the alkali metalsalts which are characterized by easy solubility, may be employed in our invention. Aszthe nitrous acid is ordinarily unstable, the use ofsalt rather than the acid in order to generate the nitrous acid in situ is preferred,

however, it is understood that the acid itself might be employed if the feature of instability is avoided.

The following resins are exemplary of those which may be stabilized in accordance with my invention. It is to be understood that this list not limiting but illustrative:

As may be seen from the examples, our stabilizing agent may be added either in the form 01' its salt in the presence of an acid or as the acid itself. As hydrochloric acid ordinarily is employed to promote the condensation of the polyvinyl compound with the aldehydes, under the a preferred conditions even though the salt has been added, it will be liberated in the reaction mixture in the form ofthe acid.

The polyvinyl acetal resins, stabilized by our process, are particularly suitable for the preparation of photographic film or any other commercial product where the transmission of light is an important -factor. Another instance or such a use is as an intermediate layer in the making of laminated or "safety glass. These stabilized resins may, also, beemployed' for making artiflcial yarn, lacquers, molding compositions, impregnated textiles or laminated products. For

instance, sheets of these stabilized resins may be laminated .with layers of wood, metal, paper, glass, cellulose ester, etc. may be employed for electrical insulation, especially where the insulated material, such as wire, is subjected to' movement or bending. In some instances it maybe found desirable to mix these stabilized polyvinyl resins with other plastic materials, such as cellulose acetate, acetate pro-.

pionate or acetate butyrate; cellulose ethers, such as ethyl cellulose, gums, other resins, either natural or synthetic, waxes and oils.

Partial polyvinyl acetal resins may be stabilized in accordance with our invention. For ex-' ample, if a polyvinyl butyraldehyde acetal resin, made by condensing butyraldehyde with polyvinyl alcohol according to French Patent No. 792,661 of Carbide and Chemicals Corporation in which from about 2.5 to about 4 molecules of polyvinyl alcohol are combined with each molecule of hu- These stabilized resins tyraldehyde, is dissolved in alcohol before heatdrying and subjected to the action of nitrous acid, a stable acetal resin results which is especially adapted to use for preparing an intermediate layer in the making of laminated glass. If desired, the acetalresin may be treated with the nitrous acid by adding it to the solution of the resin which is to be employed to make the commercial product, such as sheeting.

The acetals which may be stabilized by our process need not be complete acetals. The polyvinyl acetal resins listed herein may be either complete" acetals or they may be resins having residual acetyl and/or hydroxyl groups remaining-on the molecule.

We claim:

1. The process of stabilizing polyvinyl acetal resins which comprises subjecting a solution of a compound selected from the group consisting of the resins and the polyvinyl intermediates which are used in their preparation to the action of nitrous acid.

2. The process of stabilizing a polyvinyl acetal resin which comprises condensing an aldehyde with a polyvinyl fatty acid ester in the presence of nitrous acid.

3. The process of stabilizing a polyvinyl acetal resin which comprises treating the resin while in solution with nitrous acid.

'4. The process of stabilizing a polyvinyl acetal resin which comprises subjecting a polyvinyl acetate to the action of nitrous acid and then preparing a polyvinyl acetal therefrom.

5. The process of stabilizing polyvinyl acetal resins which comprises subjecting a solution of a compound selected from the groups consisting of the resins and the polyvinyl esters which are used in their preparation to the action of an alkali metal nitrite in the presence of an acid.

6. The process of stabilizing polyvinyl acetal resins which comprises subjecting a solution of a' compound selected from the groups consisting of the resins and the polyvinyl esters which are used in their preparation to the action of sodium nitrite in the presence of an acid.

'7. The process of preparing a polyvinyl acetal resin which comprises subjecting a polyvinyl intermediate to the action of an aldehyde and sulfoacetic acid as the condensing agent.

8. The process of stabilizing polyvinyl acetal resins'which comprises subjecting a solution of a compound selected from the group consisting of the resins of the polyvinyl intermediates which are-used in their preparation to the action of a stabilizing agent selected from the group consisting of nitrous acid and an alkali metal nitrite in the presence of an acid.

CHARLES R. FORDYCE. MARTI'I saw. 

